src/typing/merge_js.ml

(*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *)

module ImplicitInstantiationKit : Implicit_instantiation.KIT = Implicit_instantiation.Make (struct
  type output = unit

  let on_constant_tparam _ _ = ()

  let on_pinned_tparam _ _ _ = ()

  let on_missing_bounds cx name ~tparam_binder_reason ~instantiation_reason =
    Flow_js.add_output
      cx
      (Error_message.EImplicitInstantiationUnderconstrainedError
         {
           bound = Subst_name.string_of_subst_name name;
           reason_call = instantiation_reason;
           reason_l = tparam_binder_reason;
         }
      )

  let on_upper_non_t cx name u ~tparam_binder_reason ~instantiation_reason:_ =
    let msg =
      Subst_name.string_of_subst_name name
      ^ " contains a non-Type.t upper bound "
      ^ Type.string_of_use_ctor u
    in
    Flow_js.add_output
      cx
      (Error_message.EImplicitInstantiationTemporaryError
         (Reason.aloc_of_reason tparam_binder_reason, msg)
      )
end)

let detect_sketchy_null_checks cx master_cx =
  let add_error ~loc ~null_loc kind falsy_loc =
    Error_message.ESketchyNullLint { kind; loc; null_loc; falsy_loc } |> Flow_js.add_output cx
  in
  let detect_function exists_excuses loc exists_check =
    ExistsCheck.(
      let exists_excuse =
        Loc_collections.ALocMap.find_opt loc exists_excuses |> Base.Option.value ~default:empty
      in
      match exists_check.null_loc with
      | None -> ()
      | Some null_loc ->
        let add_error = add_error ~loc ~null_loc in
        if Base.Option.is_none exists_excuse.bool_loc then
          Base.Option.iter exists_check.bool_loc ~f:(add_error Lints.SketchyNullBool);
        if Base.Option.is_none exists_excuse.number_loc then
          Base.Option.iter exists_check.number_loc ~f:(add_error Lints.SketchyNullNumber);
        if Base.Option.is_none exists_excuse.string_loc then
          Base.Option.iter exists_check.string_loc ~f:(add_error Lints.SketchyNullString);
        if Base.Option.is_none exists_excuse.mixed_loc then
          Base.Option.iter exists_check.mixed_loc ~f:(add_error Lints.SketchyNullMixed);
        if Base.Option.is_none exists_excuse.enum_bool_loc then
          Base.Option.iter exists_check.enum_bool_loc ~f:(add_error Lints.SketchyNullEnumBool);
        if Base.Option.is_none exists_excuse.enum_number_loc then
          Base.Option.iter exists_check.enum_number_loc ~f:(add_error Lints.SketchyNullEnumNumber);
        if Base.Option.is_none exists_excuse.enum_string_loc then
          Base.Option.iter exists_check.enum_string_loc ~f:(add_error Lints.SketchyNullEnumString);
        ()
    )
  in
  let exists_checks =
    let open Loc_collections in
    let open ExistsCheck in
    let checks = Context.exists_checks cx in
    if not @@ ALocMap.is_empty checks then (
      let file = Context.file cx in
      let metadata = Context.metadata cx in
      let aloc_table = Utils_js.FilenameMap.find file (Context.aloc_tables cx) in
      let module_ref = Files.module_ref file in
      let ccx = Context.make_ccx master_cx in

      let reducer =
        object
          inherit
            Context_optimizer.context_optimizer
              ~no_lowers:(fun _ r -> Type.EmptyT.make r (Type.bogus_trust ())) as super

          method! type_ cx pole t =
            let open Type in
            match t with
            | ModuleT _
            | EvalT _
            | ThisClassT _
            | TypeDestructorTriggerT _
            | OpenPredT _
            | DefT
                ( _,
                  _,
                  ( InstanceT _ | ClassT _ | FunT _ | ArrT _ | ObjT _ | PolyT _
                  | ReactAbstractComponentT _ )
                ) ->
              t
            | _ -> super#type_ cx pole t
        end
      in
      let checks = ALocMap.map (Type.TypeSet.map (reducer#type_ cx Polarity.Neutral)) checks in
      Context.merge_into
        ccx
        {
          Type.TypeContext.graph = reducer#get_reduced_graph;
          trust_graph = reducer#get_reduced_trust_graph;
          property_maps = reducer#get_reduced_property_maps;
          call_props = reducer#get_reduced_call_props;
          export_maps = reducer#get_reduced_export_maps;
          evaluated = reducer#get_reduced_evaluated;
        };

      let cx =
        Context.make
          ccx
          metadata
          file
          aloc_table
          (Reason.OrdinaryName module_ref)
          Context.PostInference
      in

      let rec make_checks seen cur_checks loc t =
        let open Type in
        let open TypeUtil in
        let open Reason in
        match t with
        | AnnotT (_, t, _) -> make_checks seen cur_checks loc t
        | OpenT (_, id) when ISet.mem id seen -> cur_checks
        | OpenT (_, id) ->
          Context.find_resolved cx t
          |> Base.Option.value_map
               ~f:(make_checks (ISet.add id seen) cur_checks loc)
               ~default:cur_checks
        (* Ignore AnyTs for sketchy null checks; otherwise they'd always trigger the lint. *)
        | AnyT _ -> cur_checks
        | GenericT { bound = t; _ }
        | OpaqueT (_, { underlying_t = Some t; _ })
        | OpaqueT (_, { underlying_t = None; super_t = Some t; _ }) ->
          make_checks seen cur_checks loc t
        | MaybeT (r, t) ->
          let acc = make_checks seen cur_checks loc t in
          let acc = make_checks seen acc loc (NullT.why r (Trust.bogus_trust ())) in
          make_checks seen acc loc (VoidT.why r (Trust.bogus_trust ()))
        | OptionalT { reason = r; type_ = t; _ } ->
          let acc = make_checks seen cur_checks loc t in
          make_checks seen acc loc (VoidT.why r (Trust.bogus_trust ()))
        | UnionT (_, rep) ->
          UnionRep.members rep
          |> Base.List.fold ~f:(fun acc t -> make_checks seen acc loc t) ~init:cur_checks
        | _ ->
          let t_loc =
            let reason = reason_of_t t in
            match annot_aloc_of_reason reason with
            | Some loc -> Some loc
            | None -> Some (def_aloc_of_reason reason)
          in
          let exists_check =
            ALocMap.find_opt loc cur_checks |> Base.Option.value ~default:ExistsCheck.empty
          in
          let exists_check =
            match Type_filter.maybe t with
            | DefT (_, _, EmptyT) -> exists_check
            | _ -> { exists_check with null_loc = t_loc }
          in
          let exists_check =
            match t |> Type_filter.not_exists |> Type_filter.not_maybe with
            | DefT (_, _, BoolT _) -> { exists_check with bool_loc = t_loc }
            | DefT (_, _, StrT _) -> { exists_check with string_loc = t_loc }
            | DefT (_, _, NumT _) -> { exists_check with number_loc = t_loc }
            | DefT (_, _, MixedT _) -> { exists_check with mixed_loc = t_loc }
            | DefT (_, _, EnumT { representation_t = DefT (_, _, BoolT _); _ }) ->
              { exists_check with enum_bool_loc = t_loc }
            | DefT (_, _, EnumT { representation_t = DefT (_, _, StrT _); _ }) ->
              { exists_check with enum_string_loc = t_loc }
            | DefT (_, _, EnumT { representation_t = DefT (_, _, NumT _); _ }) ->
              { exists_check with enum_number_loc = t_loc }
            | _ -> exists_check
          in
          if exists_check = ExistsCheck.empty then
            cur_checks
          else
            ALocMap.add loc exists_check cur_checks
      in

      ALocMap.fold
        (fun loc tset acc ->
          Type.TypeSet.fold (fun t acc -> make_checks ISet.empty acc loc t) tset acc)
        checks
        ALocMap.empty
    ) else
      ALocMap.empty
  in

  Loc_collections.ALocMap.iter (detect_function (Context.exists_excuses cx)) exists_checks

let detect_test_prop_misses cx =
  let misses = Context.test_prop_get_never_hit cx in
  Base.List.iter
    ~f:(fun (prop_name, (reason_prop, reason_obj), use_op, suggestion) ->
      Flow_js.add_output
        cx
        (Error_message.EPropNotFound { prop_name; reason_prop; reason_obj; use_op; suggestion }))
    misses

let detect_unnecessary_optional_chains cx =
  Base.List.iter
    ~f:(fun (loc, lhs_reason) ->
      Flow_js.add_output cx (Error_message.EUnnecessaryOptionalChain (loc, lhs_reason)))
    (Context.unnecessary_optional_chains cx)

let detect_unnecessary_invariants cx =
  Base.List.iter
    ~f:(fun (loc, reason) ->
      Flow_js.add_output cx (Error_message.EUnnecessaryInvariant (loc, reason)))
    (Context.unnecessary_invariants cx)

let detect_invalid_type_assert_calls cx typed_ast file_sig =
  if Context.type_asserts cx then Type_asserts.detect_invalid_calls ~full_cx:cx typed_ast file_sig

let detect_es6_import_export_errors = Strict_es6_import_export.detect_errors

let detect_escaped_generics results =
  Base.List.iter
    ~f:(fun (cx, _, (_, { Flow_ast.Program.statements; _ })) ->
      Generic_escape.scan_for_escapes cx ~add_output:Flow_js.add_output statements)
    results

let detect_non_voidable_properties cx =
  (* This function approximately checks whether VoidT can flow to the provided
   * type without actually creating the flow so as not to disturb type inference.
   * Even though this is happening post-merge, it is possible to encounter an
   * unresolved tvar, in which case it conservatively returns false.
   *)
  let rec is_voidable seen_ids =
    Type.(
      function
      | OpenT (_, id) ->
        (* tvar is recursive: conservatively assume it is non-voidable *)
        if ISet.mem id seen_ids then
          false
        else (
          match Flow_js_utils.possible_types cx id with
          (* tvar has no lower bounds: we conservatively assume it's non-voidable
           * except in the special case when it also has no upper bounds
           *)
          | [] -> Flow_js_utils.possible_uses cx id = []
          (* tvar is resolved: look at voidability of the resolved type *)
          | [t] -> is_voidable (ISet.add id seen_ids) t
          (* tvar is unresolved: conservatively assume it is non-voidable *)
          | _ -> false
        )
      (* a union is voidable if any of its members are voidable *)
      | UnionT (_, rep) -> UnionRep.members rep |> List.exists (is_voidable seen_ids)
      (* an intersection is voidable if all of its members are voidable *)
      | IntersectionT (_, rep) -> InterRep.members rep |> List.for_all (is_voidable seen_ids)
      (* trivially voidable *)
      | MaybeT _
      | DefT (_, _, (VoidT | MixedT (Mixed_everything | Mixed_non_null)))
      | OptionalT _
      | AnyT _ ->
        true
      (* conservatively assume all other types are non-voidable *)
      | _ -> false
    )
  in
  let check_properties (property_map : Type.Properties.id) :
      ALoc.t Property_assignment.error list SMap.t -> unit =
    let pmap = Context.find_props cx property_map in
    SMap.iter (fun name errors ->
        let should_error =
          match NameUtils.Map.find_opt (Reason.OrdinaryName name) pmap with
          | Some (Type.Field (_, t, _)) -> not @@ is_voidable ISet.empty t
          | _ -> true
        in
        if should_error then
          List.iter
            (fun { Property_assignment.loc; desc } ->
              Flow_js.add_output cx (Error_message.EUninitializedInstanceProperty (loc, desc)))
            errors
    )
  in
  List.iter
    (fun {
           Context.public_property_map;
           private_property_map;
           errors = { Property_assignment.public_property_errors; private_property_errors };
         } ->
      check_properties public_property_map public_property_errors;
      check_properties private_property_map private_property_errors)
    (Context.voidable_checks cx)

let check_implicit_instantiations cx master_cx =
  if Context.run_post_inference_implicit_instantiation cx then
    let implicit_instantiation_checks = Context.implicit_instantiation_checks cx in
    ImplicitInstantiationKit.fold
      cx
      master_cx
      ~init:()
      ~f:(fun _ _ _ _ -> ())
      ~post:(fun ~init_cx ~cx ->
        let new_errors = Context.errors cx in
        Flow_error.ErrorSet.iter (fun error -> Context.add_error init_cx error) new_errors)
      implicit_instantiation_checks

class resolver_visitor =
  (* TODO: replace this with the context_optimizer *)
  let no_lowers _cx r = Type.Unsoundness.merged_any r in
  object (self)
    inherit [unit] Type_mapper.t_with_uses as super

    method! type_ cx map_cx t =
      let open Type in
      match t with
      | OpenT (r, id) -> Flow_js_utils.merge_tvar ~filter_empty:true ~no_lowers cx r id
      | EvalT (t', dt, _id) ->
        let t'' = self#type_ cx map_cx t' in
        let dt' = self#defer_use_type cx map_cx dt in
        if t' == t'' && dt == dt' then
          t
        else
          Flow_cache.Eval.id cx t'' dt'
      | _ -> super#type_ cx map_cx t

    (* Only called from type_ and the CreateObjWithComputedPropT use case *)
    method tvar _cx _seen _r id = id

    (* overridden in type_ *)
    method eval_id _cx _map_cx _id = assert false

    method props cx map_cx id =
      let props_map = Context.find_props cx id in
      let props_map' =
        NameUtils.Map.ident_map (Type.Property.ident_map_t (self#type_ cx map_cx)) props_map
      in
      let id' =
        if props_map == props_map' then
          id
        (* When mapping results in a new property map, we have to use a
           generated id, rather than a location from source. *)
        else
          Context.generate_property_map cx props_map'
      in
      id'

    (* These should already be fully-resolved. *)
    method exports _cx _map_cx id = id

    method call_prop cx map_cx id =
      let t = Context.find_call cx id in
      let t' = self#type_ cx map_cx t in
      if t == t' then
        id
      else
        Context.make_call_prop cx t'
  end

let detect_matching_props_violations cx =
  let open Type in
  let resolver = new resolver_visitor in
  let step (reason, key, sentinel, obj) =
    let sentinel = resolver#type_ cx () sentinel in
    match drop_generic sentinel with
    (* TODO: it should not be possible to create a MatchingPropT with a non-tvar tout *)
    | DefT (_, _, (BoolT (Some _) | StrT (Literal _) | NumT (Literal _))) ->
      let obj = resolver#type_ cx () obj in
      (* Limit the check to promitive literal sentinels *)
      let use_op =
        Op
          (MatchingProp
             {
               op = reason;
               obj = TypeUtil.reason_of_t obj;
               key;
               sentinel_reason = TypeUtil.reason_of_t sentinel;
             }
          )
      in
      (* If `obj` is a GenericT, we replace it with it's upper bound, since ultimately it will flow into
         `sentinel` rather than the other way around. *)
      Flow_js.flow cx (MatchingPropT (reason, key, sentinel), UseT (use_op, drop_generic obj))
    | _ -> ()
  in
  match Context.env_mode cx with
  | Options.SSAEnv _ ->
    let matching_props = Context.new_env_matching_props cx in
    List.iter
      (fun (prop_name, other_loc, obj_loc) ->
        let env = Context.environment cx in
        let other_t_opt = Loc_env.find_write env other_loc in
        let obj_t_opt = Loc_env.find_write env obj_loc in
        match (other_t_opt, obj_t_opt) with
        | (Some other_t, Some obj_t) ->
          step (TypeUtil.reason_of_t other_t, prop_name, other_t, obj_t)
        | _ -> failwith "Missing typing information for matching props test.")
      matching_props
  | _ ->
    let matching_props = Context.matching_props cx in
    List.iter step matching_props

let detect_literal_subtypes =
  let lb_visitor = new resolver_visitor in
  let ub_visitor =
    object (_self)
      inherit resolver_visitor as super

      method! type_ cx map_cx t =
        let open Type in
        match super#type_ cx map_cx t with
        | GenericT { bound; _ } -> bound
        | t -> t
    end
  in
  fun cx ->
    match Context.env_mode cx with
    | Options.SSAEnv _ ->
      let new_env_checks = Context.new_env_literal_subtypes cx in
      List.iter
        (fun (loc, check) ->
          let open Type in
          let env = Context.environment cx in
          let u =
            UseT (Op (Internal Refinement), New_env.New_env.provider_type_for_def_loc env loc)
          in
          let l =
            match check with
            | Env_api.SingletonNum (lit_loc, sense, num, raw) ->
              let reason = lit_loc |> Reason.(mk_reason (RNumberLit raw)) in
              DefT (reason, bogus_trust (), NumT (Literal (Some sense, (num, raw))))
            | Env_api.SingletonBool (lit_loc, b) ->
              let reason = lit_loc |> Reason.(mk_reason (RBooleanLit b)) in
              DefT (reason, bogus_trust (), BoolT (Some b))
            | Env_api.SingletonStr (lit_loc, sense, str) ->
              let reason = lit_loc |> Reason.(mk_reason (RStringLit (OrdinaryName str))) in
              DefT (reason, bogus_trust (), StrT (Literal (Some sense, Reason.OrdinaryName str)))
          in
          let l = lb_visitor#type_ cx () l in
          let u = ub_visitor#use_type cx () u in
          Flow_js.flow cx (l, u))
        new_env_checks
    | _ ->
      let checks = Context.literal_subtypes cx in
      List.iter
        (fun (t, u) ->
          let t = lb_visitor#type_ cx () t in
          let u = ub_visitor#use_type cx () u in
          Flow_js.flow cx (t, u))
        checks

let check_constrained_writes init_cx master_cx =
  let checks = Context.constrained_writes init_cx in
  if not @@ Base.List.is_empty checks then (
    let file = Context.file init_cx in
    let metadata = Context.metadata init_cx in
    let aloc_table = Utils_js.FilenameMap.find file (Context.aloc_tables init_cx) in
    let module_ref = Files.module_ref file in
    let ccx = Context.make_ccx master_cx in

    let reducer =
      let mk_reason =
        let open Reason in
        let open Utils_js in
        update_desc_reason (function
            | RIdentifier (OrdinaryName name) -> RCustom (spf "variable `%s` of unknown type" name)
            | RParameter (Some name)
            | RRestParameter (Some name) ->
              RUnknownParameter name
            | RTypeParam (name, _, _) ->
              RCustom
                (spf "unknown implicit instantiation of `%s`" (Subst_name.string_of_subst_name name))
            | desc -> desc
            )
      in
      new Context_optimizer.context_optimizer ~no_lowers:(fun _ r ->
          Type.EmptyT.make (mk_reason r) (Type.bogus_trust ())
      )
    in
    let checks =
      Base.List.map
        ~f:(fun (t, u) ->
          let t = reducer#type_ init_cx Polarity.Neutral t in
          let u = reducer#use_type init_cx Polarity.Neutral u in
          (t, u))
        checks
    in
    Context.merge_into
      ccx
      {
        Type.TypeContext.graph = reducer#get_reduced_graph;
        trust_graph = reducer#get_reduced_trust_graph;
        property_maps = reducer#get_reduced_property_maps;
        call_props = reducer#get_reduced_call_props;
        export_maps = reducer#get_reduced_export_maps;
        evaluated = reducer#get_reduced_evaluated;
      };

    let cx =
      Context.make
        ccx
        metadata
        file
        aloc_table
        (Reason.OrdinaryName module_ref)
        Context.PostInference
    in
    Base.List.iter ~f:(Flow_js.flow cx) checks;

    let new_errors = Context.errors cx in
    Flow_error.ErrorSet.iter (Context.add_error init_cx) new_errors
  )

let get_lint_severities metadata strict_mode lint_severities =
  if metadata.Context.strict || metadata.Context.strict_local then
    StrictModeSettings.fold
      (fun lint_kind lint_severities ->
        LintSettings.set_value lint_kind (Severity.Err, None) lint_severities)
      strict_mode
      lint_severities
  else
    lint_severities

(* Post-merge errors.
 *
 * At this point, all dependencies have been merged and the component has been
 * linked together. Any constraints should have already been evaluated, which
 * means we can complain about things that either haven't happened yet, or
 * which require complete knowledge of tvar bounds.
 *)
let post_merge_checks cx master_cx ast tast metadata file_sig =
  let results = [(cx, ast, tast)] in
  detect_sketchy_null_checks cx master_cx;
  detect_non_voidable_properties cx;
  check_implicit_instantiations cx master_cx;
  detect_test_prop_misses cx;
  detect_unnecessary_optional_chains cx;
  detect_unnecessary_invariants cx;
  detect_invalid_type_assert_calls cx tast file_sig;
  detect_es6_import_export_errors cx metadata results;
  detect_escaped_generics results;
  detect_matching_props_violations cx;
  detect_literal_subtypes cx;
  check_constrained_writes cx master_cx

let optimize_builtins cx =
  let reducer =
    let no_lowers _ r = Type.AnyT (r, Type.AnyError (Some Type.UnresolvedName)) in
    new Context_optimizer.context_optimizer ~no_lowers
  in
  let builtins = Context.builtins cx in
  let on_missing name t =
    let reason = TypeUtil.reason_of_t t in
    Flow_js.flow_t cx (Type.AnyT (reason, Type.AnyError (Some Type.UnresolvedName)), t);
    Flow_js.add_output
      cx
      (Error_message.EBuiltinLookupFailed { reason; name = Some name; potential_generator = None })
  in
  Builtins.optimize_entries builtins ~on_missing ~optimize:(reducer#type_ cx Polarity.Neutral);
  Context.set_graph cx reducer#get_reduced_graph;
  Context.set_trust_graph cx reducer#get_reduced_trust_graph;
  Context.set_property_maps cx reducer#get_reduced_property_maps;
  Context.set_call_props cx reducer#get_reduced_call_props;
  Context.set_export_maps cx reducer#get_reduced_export_maps;
  Context.set_evaluated cx reducer#get_reduced_evaluated